Name: high throughput co-culture assays for the investigation of microbial interactions
Uploaded: 2019-10-15T14:00:00
Description: Watch this Scientific Journal Video about High Throughput Co-culture Assays for the Investigation of Microbial Interactions at JoVE.com

We thank Daniel May, Marc Chevrette, and Don Hoang for critical reading of the manuscript. This work, including the efforts of Cameron R. Currie, was supported by the University of Wisconsin-Madison, Office of the Vice Chancellor for Research and Graduate Education with funding from the Wisconsin Alumni Research Foundation, funding also provided by the National Institutes of Health Centers for Excellence for Translational Research (U19-AI109673-01). Reed M. Stubbendieck was supported by a National Library of Medicine training grant to the Computation and Informatics in Biology and Medicine Training Program (NLM 5T15LM007359). The funders had no role in study design, data collection, and interpretation, or the decision to submit the work for publication.

Informed consent was obtained from the donor&#39;s parents, and the Human Subjects Committee at the University of Wisconsin-Madison approved the study (Institutional Review Board [IRB] approval number H-2013-1044).
1. Sample Culture
NOTE: This procedure is used here for the study of interactions among bacteria isolates from the human nasal cavity. In principle, the following methods are applicable to any culture condition. Brain-heart-infusion broth (...

<ol>
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CLSI document M02-A11. , (2012).</li><li>Adnani, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coculture+of+Marine+Invertebrate-Associated+Bacteria+and+Interdisciplinary+Technologies+Enable+Biosynthesis+and+Discovery+of+a+New+Antibiotic,+Keyicin.">Coculture of Marine Invertebrate-Associated Bacteria and Interdisciplinary Technologies Enable Biosynthesis and Discovery of a New Antibiotic, Keyicin.</a> ACS Chemical Biology. 12 (12), 3093-3102 (2017).</li><li>Nichols, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+iChip+for+high+throughput+in+situ+cultivation+of+&amp;#34;uncultivable&amp;#34;+microbial+species.">Use of iChip for high throughput in situ cultivation of &amp;#34;uncultivable&amp;#34; microbial species.</a> Applied and Environmental Microbiology. 76 (8), 2445-2450 (2010).</li><li>Gonzalez, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+competition+between+Bacillus+subtilis+and+Staphylococcus+aureus+monitored+by+imaging+mass+spectrometry.">Microbial competition between Bacillus subtilis and Staphylococcus aureus monitored by imaging mass spectrometry.</a> Microbiology (Reading, England). 157 (Pt 9), 2485-2492 (2011).</li><li>Hoefler, B. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enzymatic+resistance+to+the+lipopeptide+surfactin+as+identified+through+imaging+mass+spectrometry+of+bacterial+competition.">Enzymatic resistance to the lipopeptide surfactin as identified through imaging mass spectrometry of bacterial competition.</a> Proceedings of the National Academy of Sciences of the United States of America. 109 (32), 13082-13087 (2012).</li><li>Hoefler, B. C., Straight, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+Mass+Spectrometry,+Metabolism,+and+New+Views+of+the+Microbial+World.">Imaging Mass Spectrometry, Metabolism, and New Views of the Microbial World.</a> Natural Products Analysis. , 349-396 (2014).</li><li>Yang, Y. L., Xu, Y., Straight, P., Dorrestein, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translating+metabolic+exchange+with+imaging+mass+spectrometry.">Translating metabolic exchange with imaging mass spectrometry.</a> Nature Chemical Biology. 5 (12), 885-887 (2009).</li><li>Stubbendieck, R. 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Antibiotics and other secondary metabolites that mediate microbial interactions are useful for a multitude of applications, including drug discovery. Herein, a protocol for co-culture assays to assess large numbers of microbial interactions is presented. These co-culture interaction assays are a simple, affordable, scalable, and high throughput means to investigate many pairwise combinations of microorganisms in tandem. Target organisms are spotted next to test organisms in a well of a 12 well plate using an inoculation ...

In nature, microorganisms rarely exist in isolation; consequently, they are constantly interacting with other organisms. Therefore, studying how microorganisms interact with each other is essential to understanding a multitude of microbial behaviors1. Microbial interactions can be mutualistic, commensal, or antagonistic. These in teractions can affect not only the microorganisms themselves but also the environments and hosts that the microorganisms colonize1,2.
Many scientists study microbial interactions to identify new antimicrobial molecules. One of the first clinically important antimicrobial molecules was found through the study of microbial interactions. Sir Alexander Fleming observed a contaminating Penicillium spp. isolate that inhibited the growth of a Staphylococcus strain, which led to the discovery of the commonly used antibiotic penicillin3. Characterization of the mechanisms that microorganisms use to antagonize their competitors remains a fruitful resource for the discovery of antimicrobial molecules. For example, it was recently shown that Streptomyces sp. strain Mg1 produces antibiotic linearmycins, which have a lytic and degradative activity against Bacillus subtilis4.
Further, a non-ribosomally synthesized peptide named lugdunin was recently discovered after the observation that nasal commensal Staphylococcus lugdunensis inhibits Staphylococcus aureus5. Studies have also shown that mutualistic interactions between microorganisms are equally as powerful as antagonistic interactions for the discovery of antimicrobial molecules. For example, many fungus-farming ants in the tribe Attini harbor symbiotic bacteria called Pseudonocardia on their exoskeleton that produces antifungal molecules to inhibit an obligate pathogen of their fungal crop6. As the study of microbial interactions has been beneficial for discovering antimicrobial molecules, the use of high throughput screens may result in the discovery of new antimicrobial molecules.
With respect to the cost and ease of performance, the methodologies used to study microbial interactions range from simple to complex. For instance, an agar plug assay is an inexpensive and simple method that can be used to investigate antagonism between multiple microorganisms7. However, an agar plug assay is not an efficient procedure and can be labor-intensive for many pairwise combinations.To assess the effects of microbially produced products on target isolates of interest in a high throughput manner, many laboratories use disk diffusion assays8. These assays are easy and inexpensive and can be scalable to higher numbers of samples7. However, this assay requires the generation of microbial extracts and may produce misleading results for certain combinations of target organisms and antibiotics, such as Salmonella and cephalosporins9.
The preceding approaches rely on isolated components to elicit a response in a target organism, instead of allowing microorganisms to interact with each other. This is of note because interactions between microbes may elicit the production of &#34;cryptic&#34; antimicrobial molecules that are not produced in monoculture. For instance, it was recently shown that the antimicrobial keyicin is only produced by a Micromonospora sp. when co-cultured with a Rhodococcus sp. that is isolated from the same sponge microbiome10. More complex interaction methodologies circumvent this potential monoculture hindrance. For instance, the iChip is useful for isolating rare and difficult to cultivate bacteria from environmental samples and allows for the observation of microbial interactions through growth in situ11. To investigate interactions in detail, matrix assisted laser desorption/ionization time-of-flight imaging mass spectrometry (MALDI-TOF-IMS) can be used. This approach provides detailed information on the composition and distribution of small molecules and peptides produced by interacting microbial colonies with high spatial resolution. MALDI-TOF-IMS&#160;has also been used in multiple studies of bacterial interactions to characterize the mechanisms of competition12,13,14,15. However, MALDI-TOF-IMS often requires laborious sample preparation, specialized expertise to operate the equipment, and expensive and specialized mass spectrometers. For these reasons, it is a difficult technique to use for high throughput studies. Thus, a simple, scalable, and high throughput co-culture assay for microbial interactions that overcomes many limitations of the above approaches would be beneficial.
Here, a protocol for high throughput microbial co-culture is presented. This assay is simple and easily incorporated into preexisting studies of microbial interactions. In contrast to many commonly used methods for the study of microbial interactions, our method is simple, inexpensive, and is amenable to investigating large numbers of interactions. These assays are not only easy to perform, but the materials are widely available from most laboratory suppliers or public resources (e.g., libraries and makerspaces). Consequently, this assay is advantageous as a first line of investigation to identify and parse interesting patterns among many pairwise combinations of microorganisms, which may be especially useful for the investigation of microbial ecology.

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		<tr>
			<td>1 &#956;L disposable polystyrene inoculating loops, blue</td>
			<td>VWR</td>
			<td>12000-806</td>
			<td></td>
		</tr>
		<tr>
			<td>10 &#956;L disposable polystyrene inoculating loops, yellow</td>
			<td>VWR</td>
			<td>12000-810</td>
			<td></td>
		</tr>
		<tr>
			<td>12-well cell culture plate, sterile with lid</td>
			<td>Greiner bio-one</td>
			<td>665 180</td>
			<td></td>
		</tr>
		<tr>
			<td>14 mL polystyrene round bottom tube, 17 x 100mm style, nonpyrogenic, sterile</td>
			<td>Falcon</td>
			<td>352057</td>
			<td></td>
		</tr>
		<tr>
			<td>2.0 self standing screw cap tubes with caps, sterile</td>
			<td>USA scientific</td>
			<td>1420-9710</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mL serological pipet</td>
			<td>Cell Treat</td>
			<td>229225B</td>
			<td></td>
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			<td>Agar, bacteriological</td>
			<td>VWR</td>
			<td>J637</td>
			<td></td>
		</tr>
		<tr>
			<td>Brain Heart Infusion Broth</td>
			<td>Dot Scientific</td>
			<td>DSB11000-5000</td>
			<td></td>
		</tr>
		<tr>
			<td>Polycarbonate filament, white, 3mm diameter</td>
			<td>Keene Village Plastics</td>
			<td>12.1-3MM-WH-581.2-1KG-R</td>
			<td></td>
		</tr>
		<tr>
			<td>School Glue</td>
			<td>Elmer&#39;s</td>
			<td>EPIE304</td>
			<td></td>
		</tr>
		<tr>
			<td>Taz 6 3D printer</td>
			<td>Lulzbot</td>
			<td></td>
			<td></td>
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high throughput co-culture assays for the investigation of microbial interactions

The study of interactions between microorganisms has led to numerous discoveries, from novel antimicrobials to insights in microbial ecology. Many approaches used for the study of microbial interactions require specialized equipment and are expensive and time intensive. This paper presents a protocol for co-culture interaction assays that are inexpensive, scalable to large sample numbers, and easily adaptable to numerous experimental designs. Microorganisms are cultured together, with each well representing one pairwise combination of microorganisms. A test organism is cultured on one side of each well and first incubated in monoculture. Subsequently, target organisms are simultaneously inoculated onto the opposite side of each well using a 3D-printed inoculation stamp. After co-culture, the completed assays are scored for visual phenotypes, such as growth or inhibition. These assays can be used to confirm phenotypes or identify patterns among isolates of interest. Using this simple and effective method, users can analyze combinations of microorganisms rapidly and efficiently. This co-culture approach is applicable to antibiotic discovery as well as culture-based microbiome research and has already been successfully applied to both applications.

Co-culture interaction assays can be used to understand microbial interactions, identify patterns of interest, and uncover microbial isolates with intriguing activities. In these assays, a test organism is monocultured on one side of a 12 well agar plate and incubated for 7 days. Subsequently, a target organism is spotted next to the test organism and the two microbes were co-cultured for 7 days before scoring for the growth phenotype of the target organism. The assays are scored based on...

Watch this Scientific Journal Video about High Throughput Co-culture Assays for the Investigation of Microbial Interactions at JoVE.com

High Throughput Co-culture Assays for the Investigation of Microbial Interactions

The co-culture interaction assays presented in this protocol are inexpensive, high throughput, and simple. These assays can be used to observe microbial interactions in co-culture, identify interaction patterns, and characterize the inhibitory potential of a microbial strain of interest against human and environmental pathogens.

The study of interactions between microorganisms has led to numerous discoveries, from novel antimicrobials to insights in microbial ecology. Many ...

Our protocol provides a high throughput method for screening a large number of pairwise microbial interactions in tandem to identify interactions of interest which can aid microbiome research and antimicrobial discovery. This method is readily applicable to studying microbial interactions in a variety of systems, as long as the microorganisms are amiable to culture under laboratory conditions. The main advantage of this technique is that it allows users to screen a large number of microbial interactions in a relatively short period of time.New users of this technique should take time, especially when inoculating the bioassay plates, as it is crucial to be careful to minimize overgrowth or contamination. Visual demonstration of this technique is critical, because inoculating the bioassay plates requires precision to ensure that the organisms do not overgrow the wells, and that the co-cultures are not contaminated. Begin by preparing overnight cultures.Use a serological pipette to add three milliliters of BHI broth into 14-milliliter culture tubes. Then use a sterile one microliter inoculating loop to inoculate a bacterial colony into the broth. Swirl the loop to ensure that the clump disperses into the broth.Briefly vortex the culture tubes, and incubate them overnight at 37 degrees Celsius on a shaker at 250 RPM. Once the bacterial cultures reach an OD 600 above one, vortex them to break up the clumps of cells. Prepare PHI media with 1.5%agar, and sterilize it by autoclaving.Then cool the media to 55 degrees Celsius in a temperature-controlled water bath, and dispense three milliliters of molten BHI media into each of the 12 wells on a plate, ensuring that the wells are as even as possible. Then allow the agar to set overnight. Inoculate the test organism on a bioassay plate by inserting a sterile 10-microliter inoculating loop into the overnight culture, and streaking the culture droplet over the left third of a plate well.Repeat until all 12 wells on the plate have been inoculated. Incubate the plates upside down at the appropriate temperature for seven days. If incubating at temperatures greater than or equal to 37 degrees Celsius, or in drier climates, store the plates in a humid container to prevent them from drying out.After the six-day incubation of the bioassay plate, prepare overnight cultures of the target organism as previously described. Prepare the target plate by filling each well of an empty 12-well plate with 1.8 milliliters of BHI, and 200 microliters of the target overnight culture. Place a sterile inoculation stamp into the target plate.Gently swirl the cultures around the wells, ensuring that they do not cross-contaminate neighboring wells. Lift the inoculation stamp, and ensure that there is a droplet of diluted target culture on each stamp tip. Place the inoculation stamp on an uninoculated bioassay plate, and gently rock the stamp so that the culture droplet inoculates each well.Once the stamp is removed, a droplet of culture should be visible in the wells. If any wells are not inoculated with the inoculation stamp, spot three microliters of diluted overnight culture onto the wells using a pipette. Then inoculate the bioassay plates as previously described, but align the stamp tips with the right side of the 12-well plate, ensuring that the stamp does not contact the existing bacterial colony.Carefully remove the stamp, and place it back into the target plate. If the agar has solidified in the wells unevenly, gently rock the stamp back and forth, but be careful not to shift the stamp into the test organism growth. Repeat the inoculation for each bioassay plate until all the plates are inoculated, then incubate the plates upside down at the appropriate temperature for seven days.After co-culturing the test and target organism for one week, score the interactions based on visual assessment. Score the wells with the target organism growth that exhibits indistinguishable growth from the monoculture as zero. Score the wells with diminished growth as one, and no growth as two.The co-culture assays described here were used to assess the inhibitory activity of the actinobacteria test organisms toward the staphylococcus species target organisms isolated from the human nasal cavity. A total of 812 pairwise combinations were tested. Notably, Corynebacterium propinquum strongly inhibited coagulase negative staphylococci, particularly in comparison to other Corynebacteria that either weakly inhibited coagulase negative staphylococci or had no inhibitory effects.Through the use of comparative genomics, a biosynthetic gene cluster for siderophore production was identified in the Corynebacterium propinquum genome. Co-culture interaction assays using standard and iron-supplemented BHI medium determined that the inhibition phenotype between Corynebacterium propinquum and coagulase negative staphylococci was in fact iron-dependent. It is important to be careful when stamping the plate.Double check each well after stamping, and make sure the inoculation stamp is aligned correctly to prevent contamination. After identifying interactions of interest, subsequent studies using microbial genetics and genomics, natural product isolation and characterization, or imaging mass spectrometry can be used to characterize mechanisms underlying these interactions. This protocol has recently been used to uncover siderophore-mediated competition among the human nasal microbiota, and aided in the discovery of a new antifungal molecule called cyphomycin.

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JoVE Journal

Immunology and Infection

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since several decades, the sudden burst of multi- and extensively-drug resistant strains is a serious threat for the control of tuberculosis. Therefore, it is essential to identify new targets and pathways critical for the causative agent of the tuberculosis, Mycobacterium tuberculosis (Mtb) and to search for novel chemicals that could become TB drugs. One approach is to set&#160;up methods suitable for the genetic and chemical screens of large scale libraries enabling the search of a needle in a haystack. To this end, we developed a phenotypic assay relying on the detection of fluorescently labeled Mtb within fluorescently labeled host&#160;cells using automated confocal microscopy. This in vitro assay allows an image based quantification of the colonization process of Mtb&#160;into the host and was optimized for the 384-well microplate format, which is proper for screens of siRNA-, chemical compound- or Mtb mutant-libraries. The images are then processed for multiparametric analysis, which provides read&#160;out inferring on the pathogenesis of Mtb&#160;within host cells.

Here, we describe a phenotypic assay applicable to the High-throughput/High-content screens of small-interfering synthetic RNA (siRNA), chemical compound, and Mycobacterium tuberculosis mutant libraries. This method relies on the detection of fluorescently labeled Mycobacterium tuberculosis within fluorescently labeled host&#160;cell using automated confocal microscopy.

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since ...

High-throughput Screening for Broad-spectrum Chemical Inhibitors of RNA Viruses

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat because of increased worldwide exchanges and human populations penetrating more and more natural ecosystems. A good example of such an emerging situation is chikungunya virus epidemics of 2005-2006 in the Indian Ocean. Recent progresses in our understanding of cellular pathways controlling viral replication suggest that compounds targeting host cell functions, rather than the virus itself, could inhibit a large panel of RNA viruses. Some broad-spectrum antiviral compounds have been identified with host target-oriented assays. However, measuring the inhibition of viral replication in cell cultures using reduction of cytopathic effects as a readout still represents a paramount screening strategy. Such functional screens have been greatly improved by the development of recombinant viruses expressing reporter enzymes capable of bioluminescence such as luciferase. In the present report, we detail a high-throughput screening pipeline, which combines recombinant measles and chikungunya viruses with cellular viability assays, to identify compounds with a broad-spectrum antiviral profile.

In vitro assays to measure virus replication have been greatly improved by the development of recombinant RNA viruses expressing luciferase or other enzymes capable of bioluminescence. Here we detail a high-throughput screening pipeline that combines such recombinant strains of measles and chikungunya viruses to isolate broad-spectrum antivirals from chemical libraries.

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat ...

ScanLag: High-throughput Quantification of Colony Growth and Lag Time

Growth dynamics are fundamental characteristics of microorganisms. Quantifying growth precisely is an important goal in microbiology. Growth dynamics are affected both by the doubling time of the microorganism and by any delay in growth upon transfer from one condition to another, the lag. The ScanLag method enables the characterization of these two independent properties at the level of colonies originating each from a single cell, generating a two-dimensional distribution of the lag time and of the growth time. In ScanLag, measurement of the time it takes for colonies on conventional nutrient agar plates to be detected is automated on an array of commercial scanners controlled by an in house application. Petri dishes are placed on the scanners, and the application acquires images periodically. Automated analysis of colony growth is then done by an application that returns the appearance time and growth rate of each colony. Other parameters, such as the shape, texture and color of the colony, can be extracted for multidimensional mapping of sub-populations of cells. Finally, the method enables the retrieval of rare variants with specific growth phenotypes for further characterization. The technique could be applied in bacteriology for the identification of long lag that can cause persistence to antibiotics, as well as a general low cost technique for phenotypic screens.

ScanLag is a high-throughput method for measuring the delay in growth, namely lag time, as well as the growth rate of colonies for thousands of cells in parallel. Screening using ScanLag enables the discrimination between long lag-time and slow growth at the level of a single variant.

Growth dynamics are fundamental characteristics of microorganisms. Quantifying growth precisely is an important goal in microbiology. Growth dynamics are ...

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying Salmonella-host interactions are&#160;important to elucidate the molecular pathogenesis of Salmonella infection. The Gentamicin protection assay to phenotype Salmonella association, invasion and replication in phagocytic cells was adapted to allow high-throughput screening to define the roles of deletion mutants of Salmonella enterica serotype Typhimurium in host interactions using RAW 264.7 murine macrophages. Under this protocol, the variance in measurements is significantly reduced compared to the standard protocol, because wild-type and multiple mutant strains can be tested in the same culture dish and at the same time. The use of multichannel pipettes increases the throughput and enhances precision. Furthermore, concerns related to using less host cells per well in 96-well culture dish were addressed. Here, the protocol of the modified in vitro Salmonella invasion assay using phagocytic cells was successfully employed to phenotype 38 individual Salmonella deletion mutants for association, invasion and intracellular replication. The in vitro phenotypes are presented, some of which were subsequently confirmed to have in vivo phenotypes in an animal model. Thus, the modified, standardized assay to phenotype Salmonella association, invasion and replication in macrophages with high-throughput capacity could be utilized more broadly to study bacterial-host interactions.

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

A high-throughput assay to in vitro phenotype Salmonella or other bacterial association, invasion, and replication in phagocytic cells with high-throughput capacity was developed. The method was employed to evaluate Salmonella gene knockout mutant strains for their involvements in host-pathogen interactions.

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying ...

Microscopy-based Assays for High-throughput Screening of Host Factors Involved in Brucella Infection of Hela Cells

Brucella species are facultative intracellular pathogens that infect animals as their natural hosts. Transmission to humans is most commonly caused by direct contact with infected animals or by ingestion of contaminated food and can lead to severe chronic infections.
Brucella can invade professional and non-professional phagocytic cells and replicates within endoplasmic reticulum (ER)-derived vacuoles. The host factors required for Brucella entry into host cells, avoidance of lysosomal degradation, and replication in the ER-like compartment remain largely unknown. Here we describe two assays to identify host factors involved in Brucella entry and replication in HeLa cells. The protocols describe the use of RNA interference, while alternative screening methods could be applied. The assays are based on the detection of fluorescently labeled bacteria in fluorescently labeled host cells using automated wide-field microscopy. The fluorescent images are analyzed using a standardized image analysis pipeline in CellProfiler which allows single cell-based infection scoring.
In the endpoint assay, intracellular replication is measured two days after infection. This allows bacteria to traffic to their replicative niche where proliferation is initiated around 12 hr after bacterial entry. Brucella which have successfully established an intracellular niche will thus have strongly proliferated inside host cells. Since intracellular bacteria will greatly outnumber individual extracellular or intracellular non-replicative bacteria, a strain constitutively expressing GFP can be used. The strong GFP signal is then used to identify infected cells.
In contrast, for the entry assay it is essential to differentiate between intracellular and extracellular bacteria. Here, a strain encoding for a tetracycline-inducible GFP is used. Induction of GFP with simultaneous inactivation of extracellular bacteria by gentamicin enables the differentiation between intracellular and extracellular bacteria based on the GFP signal, with only intracellular bacteria being able to express GFP. This allows the robust detection of single intracellular bacteria before intracellular proliferation is initiated.

Microscopy-based Assays for High-throughput Screening of Host Factors Involved in Brucella Infection of Hela Cells

Two assays for microscopy-based high-throughput screening of host factors involved in Brucella infection are described. The entry assay detects host factors required for Brucella entry and the endpoint assay those required for intracellular replication. While applicable for alternative approaches, siRNA screening in HeLa cells is used to illustrate the protocols.

Brucella species are facultative intracellular pathogens that infect animals as their natural hosts. Transmission to humans is most commonly caused by ...

Electrochemiluminescence Assays for Human Islet Autoantibodies

Pinpointing islet autoantibodies associated with type 1 diabetes (T1D) leads the way to project and deter this disease in the general population. A novel ECL assay is a nonradioactive fluid phase assay for islet autoantibodies with higher sensitivity and specificity than the current 'gold' standard radio-binding assay (RBA). ECL assays can more precisely define the onset of presymptomatic T1D by distinguishing the high-risk, high-affinity autoantibodies from the low-risk, low-affinity autoantibodies generated in RBAs, and conventional enzyme-linked immunosorbent assays (ELISA). The antigen protein used in this ECL assay is labeled with Sulfo-tag and Biotin, respectively. Each ECL autoantibody assay that uses a particular antigen protein needs an optimization step before it can be used for laboratory application. This step is especially vital in determining the requirements for serum acid treatments, concentrations, and ratios of the two different antigens labeled with Sulfo-tag and Biotin. To perform the assay, serum samples are mixed with Sulfo-tag-conjugated and biotinylated capture antigen protein in phosphate buffered solution (PBS), containing 5% Bovine Serum Albumin (BSA). Afterwards, the samples are incubated overnight at 4 &#176;C. The same day, a streptavidin-coated plate is prepared with blocker buffer and incubated overnight at 4 &#176;C. On the second day, wash the streptavidin plate and transfer the serum-antigen mixture onto the plate. Place the plate on the plate shaker, set it at low speed, and incubate at room temperature for 1 h. Subsequently, the plate is washed again, and reader buffer is added. The plate is then counted on the plate reader machine. The results are conveyed through an index, which is generated from internal standard positive and negative control serum samples.

Here, we presented the methods to detect human islet autoantibodies using electrochemiluminescence (ECL) assays. The protocol, used to predict type 1 diabetes, can be expanded upon to detect autoantibodies for other autoimmune diseases.

Pinpointing islet autoantibodies associated with type 1 diabetes (T1D) leads the way to project and deter this disease in the general population. A novel ...

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella spp./Shigella spp. The gold standard method for the detection of Salmonella spp./Shigella spp. is direct culture but this is labor-intensive and time-consuming. Here, we describe a high-throughput platform for Salmonella spp./Shigella spp. screening, using real-time polymerase chain reaction (PCR) combined with guided culture. There are two major stages: real-time PCR and the guided culture. For the first stage (real-time PCR), we explain each step of the method: sample collection, pre-enrichment, DNA extraction and real-time PCR. If the real-time PCR result is positive, then the second stage (guided culture) is performed: selective culture, biochemical identification and serological characterization. We also illustrate representative results generated from it. The protocol described here would be a valuable platform for the rapid, specific, sensitive and high-throughput screening of Salmonella spp./Shigella spp.

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Salmonella spp./Shigella spp. are common pathogens attributed to diarrhea. Here, we describe a high-throughput platform for the screening of Salmonella spp./Shigella spp. using real-time PCR combined with guided culture.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella ...

High-throughput Measurement of Plasma Membrane Resealing Efficiency in Mammalian Cells

In their physiological environment, mammalian cells are often subjected to mechanical and biochemical stresses that result in plasma membrane damage. In response to these damages, complex molecular machineries rapidly reseal the plasma membrane to restore its barrier function and maintain cell survival. Despite 60 years of research in this field, we still lack a thorough understanding of the cell resealing machinery. With the goal of identifying cellular components that control plasma membrane resealing or drugs that can improve resealing, we have developed a fluorescence-based high-throughput assay that measures the plasma membrane resealing efficiency in mammalian cells cultured in microplates. As a model system for plasma membrane damage, cells are exposed to the bacterial pore-forming toxin listeriolysin O (LLO), which forms large 30-50 nm diameter proteinaceous pores in cholesterol-containing membranes. The use of a temperature-controlled multi-mode microplate reader allows for rapid and sensitive spectrofluorometric measurements in combination with brightfield and fluorescence microscopy imaging of living cells. Kinetic analysis of the fluorescence intensity emitted by a membrane impermeant nucleic acid-binding fluorochrome reflects the extent of membrane wounding and resealing at the cell population level, allowing for the calculation of the cell resealing efficiency. Fluorescence microscopy imaging allows for the enumeration of cells, which constitutively express a fluorescent chimera of the nuclear protein histone 2B, in each well of the microplate to account for potential variations in their number and allows for eventual identification of distinct cell populations. This high-throughput assay is a powerful tool expected to expand our understanding of membrane repair mechanisms via screening for host genes or exogenously added compounds that control plasma membrane resealing.

Here we describe a high-throughput fluorescence-based assay that measures the plasma membrane resealing efficiency through fluorometric and imaging analyses in living cells. This assay can be used for screening drugs or target genes that regulate plasma membrane resealing in mammalian cells.

In their physiological environment, mammalian cells are often subjected to mechanical and biochemical stresses that result in plasma membrane damage. In ...

Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions

To simulate Cryptococcus infection, amoeba, which is the natural predator of cryptococcal cells in the environment, can be used as a model for macrophages. This predatory organism, similar to macrophages, employs phagocytosis to kill internalized cells. With the aid of a confocal laser-scanning microscope, images depicting interactive moments between cryptococcal cells and amoeba are captured. The resolution power of the electron microscope also helps to reveal the ultrastructural detail of cryptococcal cells when trapped inside the amoeba food vacuole. Since phagocytosis is a continuous process, quantitative data is then integrated in the analysis to explain what happens at the timepoint when an image is captured. To be specific, relative fluorescence units are read in order to quantify the efficiency of amoeba in internalizing cryptococcal cells. For this purpose, cryptococcal cells are stained with a dye that makes them fluoresce once trapped inside the acidic environment of the food vacuole. When used together, information gathered through such techniques can provide critical information to help draw conclusions on the behavior and fate of cells when internalized by amoeba and, possibly, by other phagocytic cells.

Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions

This paper details a protocol for preparing a co-culture of cryptococcal cells and amoebae that is studied using still, fluorescent images and high-resolution transmission electron microscope images. Illustrated here is how quantitative data can complement such qualitative information.